1. Field
This disclosure relates to a stop joint for a superconducting cable, and more particularly, to a stop joint installed on a long distance line (for example, 2 km or longer) in which a long distance superconducting cable has to be installed in order to reduce a circulation distance of a cooling fluid, thereby maintaining superconducting properties.
2. Description of the Related Art
As shown in FIG. 1, a superconducting cable system includes two terminal structures 12 and 14 to which a superconducting cable 10 is connected, and a refrigerator 16 and a circulation pump 18 provided on the front side of the one terminal structure 12.
In addition, in order to extend the length of the superconducting cable 10, a plurality of intermediate pull boxes 20 is connected on the line.
In the existing superconducting cable system, a cooling flow path is formed inside the superconducting cable 10 to cause a cooling fluid (for example, liquid nitrogen) to flow. The cooling fluid is supplied to the one terminal structure 12 through a supply pipe 22, and discharged through the other terminal structure 14, and is supplied to the refrigerator 16 through a recovery pipe 24 again so as to be circulated.
Therefore, as shown in FIG. 1, at an inlet portion 26 of the superconducting cable 10 connected to the terminal structure 12 on the side provided with the refrigerator 16, the temperature of the cooling fluid is low, and the pressure thereof is high. On the other hand, at an outlet portion 28 of the super conducting cable 10 connected to the other terminal structure 14, the cooling fluid has a high temperature due to heat invasion and heat generated by the conductor as flowing along the line, and the pressure of the cooling fluid is reduced in proportion to distance.
Accordingly, the temperature increase and the pressure reduction of the cooling fluid are caused as the cooling fluid flows to the outlet portion 28 of the superconducting cable 10, so that the superconducting properties cannot be maintained. In order to solve this problem, the cooling fluid may be compensated for a reduction in the pressure of the cooling fluid supplied to the inlet portion 26 of the superconducting cable 10. However, in this case, mechanical damage occurs in the terminal structure 12 and a cryostat of the superconducting cable. Particularly, control of the pressure of the cooling fluid is performed by a circulation pump 18. Here, a capacitance of the circulation pump 18 is limited, so that there is a difficulty in maintaining the superconducting properties on the long distance line.